Variable resistor



ct. W, 1967 G. J. MUCHER 3,346,831

VARIABLE RES I S TOR Filed July 14, 1965 2 Sheets-Sheet 1 \3 GEORGE J'. MUCHER BY ,5 $M-li.

ATTORNEYS W 10, 1967 G. J. MUCHER 3,346,831

VARIABLE RESISTOR Filed July 14, 1965 2 Sheets-Sheet 2 /N I/E N 702 GEORGE :r. MUCHER BY KIM. $W Q A 7' TOENE Y6 United States Patent 3,346,831 VARIABLE RESISTOR George .1. Mucher, Rochester, N.H., assignor to Clarostat Mfg. Co., Inc., Dover, NJEL, a corporation of New York Filed July 14, 1965, Ser. No. 471,953 2 Claims (Cl. 338-145) ABSTRACT OF THE DISCLOSURE A variable resistor having a helical resistance winding which is rotated to move an electrical contact carrier which has a portion thereof within the helical groove provided by the resistance wire and a foot portion at each of its ends formed to receive and ride on the resistance element upon rotation of the resistance Wire.

Background 07 the invention Multiturn variable resistors consisting of a resistance Wire and a contact arm which is moved along the wire to traverse the various portions thereof in order to alter the value of the resistance are well known. The most common method of moving the contact arm is through use of a rotatable shaft mechanically connected with the contact arm so that rotation of the shaft will effect longitudinal movement of the contact arm. Such an assembly is utilized in equipment wherein high accuracies are sought and the movement of the contact arm must be accom plished so that little or no electrical error can result from the mechanical construction of the device.

Summary 0 the invention A multiturn variable resistor having a casing, a nonconducting drum supported in said casing rotatably, a helically wound resistance element supported by said drum, a continous helical track formed between adjacent turns of said resistance element, a non-conducting contact carrier, means preventing relative rotational movement of said contact carrier with respect to the housing such that the contact carrier advances longitudinally along the housing, a conducting resilient arm sup ported by said contact carrier, a contact portion of said resilient arm in Wiping engagement with said resistance element, a second contact portion of said resilient arm, a collector rail in wiping contact with said second contact portion, said contact carrier being generally circular in the form of a split ring with a bore diameter slightly greater than the diameter of said track with a width slightly less than the width of said track whereby it is disposed with a substantial portion of its bore periphery in said track, a foot portion of said contact carrier at each of its ends having a width greater than the width of said track and each of said foot portions having an arcuate groove formed in its surface which can receive and ride on said resistance element upon rotation of said drum.

Description of the drawings FIG. 1 is a longitudinal elevation of a variable resistor constructed in accordance with the teachings of this invention;

3,346,831 Patented Oct. 10, 1967 FIG. 2 is an exploded perspective view of the variable resistor shown in FIG. 1 with portions thereof broken away to disclose detail views of portions thereof;

FIG. 3 is a longitudinal view with portions thereof cut away;

FIG. 4 is a partially sectional view taken along the line 44 in the direction of the arrows in FIG. 3;

FIG. 5 is a face view of the contact fingers taken along the line 55 in the direction of the arrows in FIG. 3; and

FIG. 6 is a view of the contact carrier and movable contact with portions of the winding shown dotted in.

A variable resistor constructed in accordance ,with the teachings of this invention is shown in the figures and indicated therein generally by the numeral 10. As shown, the device includes a casing 11, cylindrical drum 12, front drum face 13, rear drum face 14 and contact carrier 15. The casing is substantially cylindrical with a flattened bottom portion 11a. The front drum face 13 is substantially cylindrical providing a closure of one end of the casing with the exception of opening 13a through which shaft 16 extends in the assembled form of the device. Rear drum face 14 is substantially identical in form to front drum face 13, however, it does not contain a central opening since it provides the rear closure of the device and it is not necessary for a shaft to extend therethrough.

The cylindrical drum 12 is provided with a helical groove continuously formed in the outer face thereof which is indicated in the figures by the numeral 17. It is noted that groove 17 receives a helically wound resistance element 19 which extends throughout the length of groove 17 and which is terminated at 19a and 19b by insulated conductors 20 and 21, respectively. The groove 17 is shallow so that the resistance element 19 extends outwardly thereof providing a track 18 formed by the resistance element. Track 18 is helical.

Shaft 16 extends through externally threaded bushing 22 and knurled portion 16a thereof is embedded within drum 12 and held in by knurling which imparts the necessary turning torque and prevents backlash allowing for rotation of drum 12 upon rotation of shaft 16. The shaft is maintained in position Within the casing by nuts 23 and 24 which are threaded on the threaded portion of bushing 22 and which in the assembled condition of the device firmly grasps the end of shaft 16 and the front drum face 13 with the shaft 16 extending through the bushing and the front drum. The bushing maintains the shaft in position in a manner which is familiar to the art.

The resistance element and drum 12 are therefore supported in cantilever manner with the rear end of the drum provided with concentrically spaced conducting rings 25 and 26 to which are attached leads 20 and 21, respectively. It is noted that lead 21 extends longitudinally of the assembly within groove 27 formed in drum 12. The manner of attachment of terminal 20 to ring 25 and terminating lead 21 to ring 26 is shown with a portion 25a and a portion 26a of rings 25 and 26 extending forwardly through the nonconducting disk which supports them as part of the drum and which is indicated by the numeral 28.

The rear drum face 14 is provided with contact fingers 29 and 30 which are resilient members electrically connected and forming outwardly projecting terminal 31. Contact fingers 29 and 30 are located apart and Wipe the surface of ring 25 upon rotation of the drum. As it is obvious, one end of the resistance element is terminated at 31 and the remaining end of the resistance element is terminated at 32 by means of resilient fingers 33 and 34 which are mounted 180 apart and joined electrically, wiping contact ring 26 upon rotation of the drum 12. The rings 25 and 26, therefore, can be referred to as slip rings and the contact finger members 29, 30, 33 and 34 can be referred to as conducting fingers. Contact carrier is formed of a thin nylon thermoplastic material of high dielectric strength, high arc resistance, high impact strength, dimensional stability, and high creep resistance. The contact carrier 15 is generally circular in the form of a split ring with a bore diameter slightly greater than the diameter of helical track 18 and a width slightly less than the width of said helical track 18 so that it can be disposed with a substantial portion of its bore periphery in track 18. Each of its ends is provided with an enlarged foot portion and these feet are designated in the figures by the numerals 15' and 15", respectively. Each of the feet is provided with an outer contour complementary to the inner contour of the case 11 so that contact carrier 15 is prevented from rotating within the case when shaft 16 is rotated so that rotation of shaft 16 will result in longitudinal movement of the contact carrier as will be explained below.

Each of the feet is provided in its upper surface with an arcuate portion for receipt of a portion of a turn of the helical wire. Hence, it is seen in FIG. 4 that foot 15' is provided with arcuate portion 15'a receiving a portion of turn 19a of helical wire 19. Likewise, foot 15" is provided with an arcuate portion 15"a receiving a portion of turn 1% of coil 19. It is noted that coils 19a and 19b are on either or have sandwiched between them coil 190 which is in contact with contact member 42. Contact member 42 is resilient and has a contact 43 and a cylindrical portion 44 which encompasses pin 39 which is fastened to foot 15'. Contact 43 lies between feet 15 and 15" and does not touch either of turns 19a or 1912 but rather only contacts turn 190 of the resistance wire. Contacts 45 and 46 are provided on the contact member 42 and these are mounted on the end of resilient arm 47 beneath contact carrier 15.

A collector rail 48 is provided extending longitudinally of the casing in the base 11a thereof and in the final assembly contacts 45 and 46 are in wiping engagement with collector rail 48 while contact 43 is in wiping engagement with helical resistance element 19 with contact 43 yieldingly urged against the resistance element and contact portions 45 and 46 yieldingly urged against the collector rail 48 by means of the resiliency of the contact member 42.

The drum may therefore be rotated and relative rotational motion between the contact carrier and the drum is prevented resulting in the longitudinal movement of the contact carrier whereby the collector rail 48 is wiped by contacts 45 and 46 while contact 43 wipes the resistance element throughout its length since the resistance element is continually rotated into contact with the contact member 43. It is noted that collector rail 48 forms the center contact of the resistance configuration and that rotation of shaft 16 varies the resistance between contact rail 48 and either of the terminals 31 and 32,

Positive stop means are provided to arrest the movement of contact carrier 15 at either end of its travel longi; tudinally within the casing. It is noted that a stop member of disk 51 is provided and mounted at the rear end of drum 12 with a portion 51a projecting radially thereof. A like stop ring 52 with projecting portion 52a is mounted on the drum at the front end with the resistance element wholly between stop members 51 and 52. It is further noted that the inner face of foot 15 will arrest further rotational movement of stop 51a at one end of movement of the contact carrier and face 116 of foot 15" will arrest further rotational movement when stop 52:: abuts it. Therefore, in the final assembly, upon the completion of the longitudinal movement of the contact carrier 15 in either direction, the continued or further movement of the contact carrier will be arrested by the stop face at the end furthermost in the direction of travel contacting the projecting portion of the respective stop ring or member.

Thus, among others, the several objects in the invention, as specifically a-forenoted, are achieved. Obviously, numerous changes in construction and rearrangement of parts might be resorted to without departing from the spirit of the invention as defined 'by the claims.

I claim:

1. In a multit'urn variable resistor, a casing, a non-conducting drum rotatably supported in said casing, a helically wound resistance element supported by said drum, a continuous helical track formed between adjacent turns of said resistance element, a non-conducting contact carrier, means preventing relative rotational movement of said contact carrier with respect to the housing such that the contact carrier advances longitudinally along the housing, a conducting resilient arm supported :by said contact carrier, a contact portion of said resilient arm in wiping engagement with said resistance element, a second contact portion of said resilient arm, a collector rail in wiping contact with said second contact portion, said contact carrier being generally circular in the form of a split ring with a bore diameter slightly greater than the diameter of said track with a width slightly less than the width of said track whereby it is disposed with a substantial portion of its bore periphery in said track, a foot portion of said contact carrier at each of its ends having a width greater than the Width of said track and each of said foot portions having an arcuate groove formed in its surface which can receive and ride on said resistance element upon rotation of said drum.

2. A variable resistor in accordance with claim 1 in which said resilient arm is supported by attachment to one of said foot portions.

References Cited UNITED STATES PATENTS 4/1925 Camp 338 8/1946 Kunz 338 -145 X 

1. IN A MULTITURN VARIABLE RESISTOR, A CASING, A NON-CONDUCTING DRUM ROTATABLY SUPPORTED IN SAID CASING, A HELICALLY WOUND RESISTANCE ELEMENT SUPPORTED BY SAID DRUM, A CONTINUOUS HELICAL TRACK FORMED BETWEEN ADJACENT TURNS OF SAID RESISTANCE ELEMENT, A NON-CONDUCTING CONTACT CARREIER, MEANS PREVENTING RELATIVE ROTATIONAL MOVEMENT OF SAID CONTACT CARRIER WITH RESPECT TO THE HOUSING SUCH THAT THE CONTACT CARRIER ADVANCES LONGITUDINALLY ALONG THE HOUSING, A CONDUCTING RESILEIENT ARM SUPPORTED BY SAID CONTACT CARRIER, A CONTACT PORTION OF SAID RESLIENT ARM IN WIPING ENGAGEMENT WITH SAID RESISTANCE ELEMENT, A SCEOND CONTACT PORTION OF SAID RESILIENT ARM A COLLECTOR RAIL IN WIPING CONTACT WITH SAID SECOND CONTACT PORTION, SAID CONTACT CARRIER BEING GENERALLY CIRCULAR IN THE FORM OF A SPLIT RING WITH A BORE DIAMETER SLIGHTLY GREATER THAN THE DIAMETER OF SAID TRACK WITH A WIDTH SLIGHTLY LESS THAN THE WIDTH OF SAID TRACK WHEREBY IT IS DISPOSED WITH A SUBSTANTIAL PORTION OF ITS BORE PERIPHERY IN SAID TRACK, A FOOT PORTION OF SAID CONTACT CARRIER AT EACH OF ITS ENDS HAVING A WIDTH GREATER THAN 